1. Field of the Invention
The present invention relates to a method for laser cutting. More particularly, the invention comprises a novel method for cutting three-dimensional (3-D) objects from solid blocks by inner cutting. The method is particularly useful for rapidly producing prototypes of solid or hollow shell objects.
Globalization and requirements for customization have brought intensive competition to into the manufacturing field. The requirements for upgrades to existing products as well as the rapid introduction of new products in a competitive market has placed great stress on product developers. To maintain their competitive edge, manufacturers have been forced to seek better ways to create evaluation prototypes of proposed design changes to exiting products as well as totally new products. In recent years, design efforts have been focused on the use of Computer Aided Design (CAD) systems. Methods for directly converting CAD output files into prototypes are very desirable and have been eagerly sought. Starting in the late 1980s, a new field of endeavor, Rapid Prototyping Manufacturing (RPM) first appeared in the United States. The essence of RPM methods is to allow direct conversion of CAD system outputs directly into solid prototypes. One method for accomplishing this process is to xe2x80x9cgrowxe2x80x9d the prototype thereby eliminating the need for molds, fixtures, jigs, fixtures, or other specialized machining equipment. The solid models resulting from this process may then be observed, evaluated, and/or tested. In addition, the solid prototypes may be turned into xe2x80x9chardxe2x80x9d (e.g., metal) parts by precision casting or other similar processes.
There are many different prototyping methods currently available for use. These may be divided into two broad categories. The first involves growing a solid shape by adding material, bit-by-bit in a controlled manner. Examples of this class of method included stereo lithography using a Stereo Lithographic Apparatus (SLA), Selective Laser Sintering (SLS) and Fused-Deposition Modeling (FDM). The second category involves adding materials in thin layers to form the desired shape. These methods are best represented by the Laminated Object Manufacturing (LOM) technique.
In stereo lithography, a CAD 3-D model is first sliced into thin layers using software well known to those skilled in the 3-D modeling arts. A laser beam at an appropriate wavelength is controlled to selectively scan the surface of a pool of photosensitive resin. The result is that the laser beam cures and solidifies the surface layer of the resin on a platform in accordance with the shape of the defined slice of the model currently being processed. The process starts with the bottom layer and, after a layer is defined and cured, the platform is incrementally lowered, the platform travel being defined by the thickness of the computer-generated layers. This allows the liquid resin in the pool to cover the solidifying layer. These process steps are repeated until the desired three-dimensional object is complete.
This process differs from the inventive prototyping process in that while the laser beam scans only the surface of the material being formed into an object, in effect, every point within the volume of the solid being produced must ultimately be scanned. This requires a relatively long time to accomplish and uses large amounts of electrical energy. The inventive process, on the other hand, must only trace the contour of the required solid within a solid volume from which the prototype object is being formed. This requires significantly less time and uses much less energy. RPM is currently a vigorously researched field because it still promises shorting development cycles.
Currently used rapid prototyping technologies have the following limitations: First, process times are deemed excessively long. To make a relatively large part with complex geometry can take a few days to a whole week. The reason for this low productivity lies in the volume scan characteristic of methods of the prior art which require the laser beams to scan every point inside the shape being formed. Typically, the focal point of a laser beam is around 0.1 mm or less. Consequently, the total scanning path will be very long contributing to the long processing time and high-energy consumption.
Second, prototype part precision is usually compromised. Cured layers are prone to warp, especially when in large parts. Also, the contraction of resin during laser curing process in the SLA method as well as possible paper distortion after absorbing moisture in the LOM method may seriously affect the precision of the finished parts.
Third, the necessary equipment required to practice the methods of the prior art are is usually quite complex. All of the rapid prototyping methods described hereinabove invariably require a moving platform which must be specially designed, thus adding to the investment in equipment.
Forth, the complexity of the shapes which may be created using prior art methods is limited. The inner-cutting method of the present invention can, however, follow very intricate geometries in a single surface scan, and is even able to cut out an enclosed shell inside another enclosed shell.
2. Discussion of the Related Art
U.S. Pat. No. 3,715,734 for MEMORY STORAGE DEVICE AND METHOD OF MAKING SAME, issued Feb. 6, 1973 to Jack Fajans, teaches a method whereby a laser may selectively carbonize spots within a block of polymethylmethacrylate. The carbonized spots so formed may later be xe2x80x9creadxe2x80x9d as binary data. FAJANS teaches no method for cleaving a three-dimensional object from within a block of suitable material by means of a dilated, suitably focused laser beam.
Several United States patents have been issued which address the use of a laser to physically change an interior point within a solid which is transparent to the wavelength of the laser. For example, U.S. Pat. No. 4,092,518 for METHOD OF DECORATING A TRANSPARENT PLASTIC MATERIAL ARTICLE BY MEANS OF A LASER BEAM, issued May 30, 1978 to Rene"" Remy Merard; U.S. Pat. No. 5,575,936 for PROCESS AND APPARATUS FOR ETCHING AN IMAGE WITHIN A SOLID ARTICLE, issued Nov. 19, 1996 to Boris Goldfarb; U.S. Pat. No. 5,637,244 for METHOD AND APPARATUS FOR CREATING AN IMAGE BY A PULSED LASER BEAM INSIDE A TRANSPARENT MATERIAL, issued Jun. 10, 1997 to Alexander I. Erokhin; U.S. Pat. No. 5,786,560 for 3-DIMENSIONAL MICROMACHINING WITH FEMTOSECOND LASER PULSES, issued Jul. 28, 1998 to Abdelkrim Tatah, et al.; and U.S. Pat. No. 5,886,318 for METHOD FOR LASER-ASSISTED IMAGE FORMATION IN TRANSPARENT OBJECTS, issued Mar. 23, 1999 to Anatoly Valentinovich Vasiliev, all teach methods for forming a viewable image inside a solid piece of a transparent material. However, none of these patents teaches or suggests a method for forming a three-dimensional, solid or hollow shell shape within a block of transparent material. The instant invention, on the other hand, teaches an apparatus and method whereby a solid object may be completely formed inside a block of a suitable transparent material.
U.S. Pat. No. 4,546,231 for CREATION OF A PARTING ZONE IN A CRYSTAL STRUCTURE, issued Oct. 8, 1985 to Herbert D. Gresser, et al. teaches the use of a laser beam to create a parting zone in a crystalline material such as diamond. An energy-transmissive window is first prepared on the outside of the crystal. This window transmits the energy of a laser beam to successive damage zones, typically adjacent one another whereby the crystal structure is destroyed. The crystal may then easily be fractured along the parting zone created by the successive damage zones. In contradistinction, the instant invention provides for the formation of a solid, three-dimensional object totally within a block of transparent material. There is no reliance on the material being crystalline. The inventive formation process relies upon carbonization of a series of sites within the transparent material which define the surface of the desired three-dimensional object being formed.
U.S. Pat. No. 5,247,923 for METHOD OF FORMING A DIAMOND DRILL BIT ELEMENT USING LASER TRIMMING, issued Sep. 28, 1993 to Maurice P. Lebourg, teaches a method similar to that of GRESSER, et al. described hereinabove. Desired cut lines within a diamond crystal are identified and selectively removed leaving a series of truncated conical structures, eventually, after successive cuts, resulting in a drill bit having a predetermined shape. Unlike the apparatus and method of the present invention, no internal, three-dimensional shape is formed in a solid block of non-crystalline material.
None of the above inventions and patents, taken either singly or in combination, is, however, seen to anticipate or suggest the instant invention as claimed.
The present invention relates to an apparatus and method for forming a solid, three-dimensional object within a block of transparent material by means of a laser beam. This invention is particularly useful in the field of rapid prototype manufacturing (RPM) wherein a computer-generated CAD file defining an object may be converted directly to the described object using the inventive method. Because only the surface of the volume being cut from the solid block must be scanned by the laser beam, the inventive process is much faster than other RPM manufacturing techniques, such as SLA or SLS, wherein a laser beam is required to scan every point inside the shape being formed. This saves large amounts of time and electrical energy over methods of the prior art. In addition, parts having complex geometries and/or part having hollow shells may readily be formed.
Accordingly, it is a principal object of the invention to provide a rapid prototyping method for forming a three-dimensional object within a block of transparent material using a laser beam.
It is another object of the invention to provide a rapid prototyping method using a laser beam wherein all cutting is accomplished in a single scan of the surface of the object being formed.
It is a further object of the invention to provide a rapid prototyping method using a laser beam which can quickly form the desired part using minimum energy.
Still another object of the invention is to provide a rapid prototyping method using a laser beam which requires a relatively small capital investment.
An additional object of the invention is to provide a rapid prototyping method using a laser beam which can produce objects having complex geometries.
It is again an object of the invention to provide a rapid prototyping method using a laser beam which can produce hollow objects.
It is a still further object of the invention to provide a rapid prototyping method using a laser beam which avoids forming the desired object from individual layers of material such as the LOM method, or by accumulating material bit-by-bit, such as the SLA or SLS methods of rapid prototyping.
It is yet another object of the invention to provide a rapid prototyping method using a laser beam which forms object having high strength and good mechanical stability.
It is an additional object of the invention to provide a rapid prototyping method using a laser beam which may be practiced in conjunction with standard numerically-controlled machine tools, such as milling machines and lathes with added laser beam generators and optical systems.
It is another object of the invention to provide a rapid prototyping method using a laser beam wherein the desired part is formed directly from a computer-aided design (CAD) file.
It is an additional object of the invention to provide a rapid prototyping method which can simultaneously forms both positive and negative prototype molds during a single scan.
It is yet another object of the invention to provide a rapid prototyping method which provides an easy correction of focal point location differences caused by the refractive index of the bulk material being machined.
It is a still further object of the invention to provide a rapid prototyping method using a laser beam which is inexpensive to implement and operate and which may be easily used.
These and other objects of the present invention will become readily apparent upon further review of the following specification and drawings.